Preparation method for silicon-carbon composite negative electrode material

Abstract

The invention discloses a preparation method of silicon-carbon composite negative electrode material, relates to the field of negative electrode materials preparation The method includes the following steps: mixing starch with water, and carrying out stirring, dispersing, cooling and standing; soaking a mixture in an ethanol solution and absolute ethyl alcohol, collecting a white solid, performing supercritical drying, crushing, then mixing the solid with a carbon source, keeping the temperature at 180-300° C., 450-600° C., and then 1000-1200° C., carrying out cooling to room temperature, and mixing a carbonized material with a graphite negative electrode material. According to the invention, the elastic material is used to improve electric conduction and achieve lithium storage. When it is filled between the coating layer and the silicon material, good conductivity is kept, effects of silicon can be used, and the defects of silicon can be avoided at the same time.

What is claimed is: 
     
         1 . A preparing method for silicon-carbon composite negative electrode material, comprising:
 step1: putting a nano-silicon and water into the disperser, according to a mass ratio of 1: (0.5-5) and dispersing evenly to obtain the nano-silicon aqueous solution;   step 2: mixing starch and water according to the mass ratio of 1: (0.1-10), and stirring for 1-20 minutes at a temperature of 85-95° C.; at the same time;   step 3: adding the nano-silicon aqueous solution and a starch solution obtained by step 2 into the disperser according to the mass ratio of nano-silicon and starch (0.5-5): (0.1-10), and dispersing evenly to form a gel solution;   step 4: cooling the gel solution to room temperature and standing for 8-48 hours;   step 5: soaking the gel solution with ethanol solution until a gel turning into a white solid, and then using absolute ethanol to soaking the white solid for 1 to 24 hours, and collecting the white solid;   step 6: putting the white solid into a supercritical dryer for drying, and crushing the dried white solid to D50=13-25 microns;   step 7: uniformly mixing a pulverized material obtained by step 6 with the carbon source according to a mass ratio of (2˜15): 1;   step 8: heating a mixed material obtained by step 7 in a reactor to 180-400° C. at a rate of no more than 10° C. per minute, keeping temperature constant for 1-3 hours, and continue to heat up to 450-600° C. at a rate of no more than 5° C. per minute, keep temperature constant for 1 to 3 hours, stirring at a speed of 100 to 200 rpm in the whole process, and at the same time passing through the protective gas to complete the carbon source coating, cooling to room temperature, and obtaining a coated material;   step 9: heating the coated material to 1000-1200°° C. at a rate of no more than 6° C. per minute in a protective gas atmosphere, keeping temperature constant for 1-5 hours, and cooling to room temperature to obtain a carbonized material;   step 10: mixing the carbonized material with a graphite negative electrode material to obtain a silicon-carbon composite negative electrode material.   
     
     
         2 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the carbon source of step 7 is selected of pitch, resin or sucrose. 
     
     
         3 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the mixed material obtained by step 7 is heated to 400° C. at a rate of no more than 10° C. per minute, in step 8. 
     
     
         4 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the mixed material is continued to heat up to 600° C. at a rate of no more than 5° C. per minute, in step 8. 
     
     
         5 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the protective gas used in step 8 is selected one or more of nitrogen, helium, neon, argon, krypton, xenon and radon. 
     
     
         6 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the protective gas used in step 9 is selected one or more of nitrogen, helium, neon, argon, krypton, xenon and radon. 
     
     
         7 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the coated material is heated to 1050-1150° C. at a rate of no more than 6° C. per minute, in step 9. 
     
     
         8 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the coated material is heated to 1100° C. at a rate of no more than 6° C. per minute, in step 9. 
     
     
         9 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the graphite negative electrode material in step 10 is an artificial graphite negative electrode material or a natural graphite negative electrode material. 
     
     
         10 . The preparing method for silicon-carbon composite negative electrode material according to  claim 1 , wherein the carbonized material is mixed with the graphite negative electrode material according to a mass ratio of 1: (1-99), in step 10.